[15.02] The Orbits of the Major Saturnian Satellites and the Gravity Field of the Saturnian System

In preparation for the Cassini Tour of the Saturnian system
Jacobson (2004 {\em AJ}\, 128, 492) developed ephemerides
for the Saturnian satellites based on numerical integrations
of their orbits fit to Earth-based astrometry and
observations acquired with the Pioneer~11 and Voyager
spacecraft. A byproduct of this effort was a revised
Saturnian system gravity field. We have extended this work
to include Cassini Doppler tracking data, radiometric range,
and optical navigation imaging. We find significant
corrections to the orbits of Mimas, Enceladus, Hyperion,
Iapetus, Phoebe, Helene, Telesto, and Calypso. Changes in
the gravity field, however, are minimal with the exception
of the GM of Phoebe. Analysis of data from the Cassini
2070 km altitude flyby of Phoebe leads to a value of
0.5527\,±,0.0010 km3 s-2 for the Phoebe GM.

The refinement of the satellite orbits will continue
throughout the Cassini tour. Planned low altitude flybys of
Enceladus, Dione, Rhea, Titan, Hyperion, and Iapetus will
permit improvement in the knowledge of their GMs.